This SLOT is not working...

[icx]

I'm trying to make a really simple application: while I'm writing in this QTextEdit, a QLabel need to be constantly updated and show how many characters the users can still write (similar to Twitter). The Clear button works well, but I can't make a slot to change the text of the QLabel as the user is writing.

I've attached below the sources.

main.cpp
widget.cpp
widget.h

I know that in widget.h I should have used the Q_OBJECT macro, but when I use it I get some "undefined reference to `vtable for MainWidget`" errors. So this following code won't work:

class MainWidget : public QWidget{
    Q_OBJECT
 
    QTextEdit *t;
    QVBoxLayout *_v;
    QString *str;
 
public:
    MainWidget();
    ~MainWidget();
 
public slots:
    void nothing(QString *s, QTextEdit *text){
        *s = text->toPlainText();
    }
};

class MainWidget : public QWidget{
    Q_OBJECT

    QTextEdit *t;
    QVBoxLayout *_v;
    QString *str;

public:
    MainWidget();
    ~MainWidget();

public slots:
    void nothing(QString *s, QTextEdit *text){
        *s = text->toPlainText();
    }
};

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[Lykurg]

Don't create a QString on the heap, better create it on the stack since it is implicit shared the data will be on the "heap" but you avoid a lot of possible errors. Next, you can't pass values via a connect. you have to get the values in your slot or use a proper signal. And if Q_OBJECT causes errors you have to recompile your project.